That law followed a chemical leak in Bhopal, India, that killed more than 1,700 people and another in West Virginia that led to an evacuation. Ammonium nitrate has been responsible for some of the largest industrial disasters in history. In fact, what remains the worst industrial accident in the nation’s history was an ammonium nitrate-triggered explosion in 1947 that killed more than 570 people in Texas City, Texas, and injured about 5,000.

But times have changed. Fears of chemical spills have given way to fears of terrorism.

In Hawaii, for example, officials said people must prove a “need to know” before they can obtain information. Though the state did not respond to a request for an explanation, the policy echoed others that cited a 2007 federal law intended to protect chemical plants from terrorist attacks. But the need-to-know requirement does not apply to the data submitted for Emergency Planning and Community Right-to-Know, said Bob Stephan, a former Homeland Security Department assistant secretary who was in charge of the U.S. government’s chemical facility anti-terrorism program from 2007-09.

“They are giving you incorrect information or incorrect rationale for not providing the data,” Stephan said.

Under Hawaii’s interpretation of the law, people who want information about specific chemical facilities near their homes are qualified to see it. But that presupposes they already know enough to ask. Clarence Martin of the state’s Hazard Evaluation and Emergency Response Office said people deserve to know what’s in their neighborhoods.

But, he added, “I’m not going to let you tell them.”

Even when the information is available, though, it’s not always accurate. Years of lax oversight and scant enforcement have resulted in shoddy records. Hundreds of companies listed approximate or inaccurate amounts of dangerous chemicals, not just ammonium nitrate.

For instance, data from Louisiana said a Jimmy Sanders Inc. facility stored nearly 50 million pounds of ammonium nitrate. But the company said it never had any at all.

Others misidentified their locations. One plant in Tucson, Ariz., listed an ambiguous address (“end of cement plant road”) and a geographic coordinate so off base that the Environmental Protection Agency’s reporting software flagged the facility as being in a different county.

Arkansas reported that the Polk County Farmers Association stored 50,000 pounds of ammonium nitrate in the rural town of Mena. But the store’s manager, Paul Stanley, said it had been moved to a facility about three miles outside of town years ago.

“I’m happy that it’s not in town,” he said, “because people don’t understand it and they jump to conclusions.”

Wisconsin documents showed that the C. Reiss Coal Co.’s facility had stored tons of ammonium nitrate in a facility in Sheboygan last year. But people would be hard pressed to use that information when deciding where to buy a home or send their kids to school. That’s because state officials say the facility is inactive and should not have been on the list.

The fertilizer building that exploded in West had been there since 1962. As the years passed, a nursing home, school and apartment buildings sprung up nearby. Townspeople thought little of the facility; it was as common a sight in the farming community as a tractor driving down the road.

The company filed the required reports listing the hazardous chemicals on site. There’s no indication that the documents were incorrect. But the county’s emergency planners had not read them.

The Monroe County Co-Op in Aberdeen, Miss., stored as much as 1 million pounds last year, according to state records. But David Hodges, the store manager, said he had about half that on site and has sold it for about 50 years without a problem.

“I’ve been here, oh, 34, 35 years, and it’s always been there,” said Larry Middleton, a retired English teacher who lives up the street and visits to buy weed remover and snake repellent.

Horton said the same about the building in Shelby. Many townspeople have lived there all their lives, he said, and the fertilizer has been there, too. Though he didn’t think most people knew the explosive potential, he said he feared that public knowledge of the building’s contents would attract terrorists.

“I can’t predict when an accident is going to happen. It just happens,” he said. “Terrorists are actively seeking ways to harm us.”

Behavioral scientists call this “probability neglect”: People are far more likely to overreact to emotional, extremely unlikely events such as terrorism than to address potential problems that are far more likely to occur.

What’s more, people are more afraid of risks brought on by outsiders, like terrorists, than threats closer to home. In experiments, people were more outraged by the thought of being exposed to radiation from nuclear waste than from radon in their own basements — even when they were told the danger was the same and the likelihood of radon exposure was much higher.

“It’s been here all this time,” Middleton said, “and nothing has happened.”